Glaucoma affects about 70 million people worldwide, and is a disorder associated with high pressure in the eye resulting in the generation of excess intraocular fluid (aqueous humor). Aqueous humor is produced at a rate of 2-3 μl/min by the ciliary body and it maintains constant intraocular pressure (IOP) around 12-20 mm Hg. Aqueous humor exits the eye primarily through the trabecular meshwork and Schlemm's canal, where it eventually drains to the episcleral veins. Maintaining intraocular pressure within appropriate ranges is critical to health of the eye, and depends on aqueous hunter dynamics, namely the production rate from the ciliary body (aqueous humor inflow) and its outflow rate through the trabeculum. The most frequent glaucoma is called open-angle glaucoma, and results from an increase in the fluidic resistance of the trabecular meshwork. Left untreated, this disease typically causes damage to the optic nerve, with consequent loss of vision, initially peripheral, but progressively leading to total blindness. Unfortunately, glaucoma is often asymptomatic until late in the progress of the disease.
Traditionally, glaucoma is treated using medication, for example, the daily application of eye drops, such as Brinzolamide ophthalmic, that reduce production of aqueous humor. Such medications do not cure glaucoma, and must be continue to be taken to maintain intraocular pressures within accepted limits. In certain cases, such treatment may fail and other surgical treatments are employed, such as filter procedures or placement of a glaucoma drainage device. Glaucoma drainage devices reduce intraocular fluid pressure by providing an artificial drainage pathway, thus maintaining a low intraocular pressure (“IOP”).
Previously-known glaucoma drainage devices usually comprise a structure having a drainage tube that is inserted through a small incision made in the conjunctiva. The surgeon then makes a tiny incision in the sclera of the eye and creates an opening for the drainage implant device. The drainage tube is placed such that the opening of the tube is disposed in the anterior chamber of the eye within the aqueous humor. The tube is sutured in place with the drainage device attached to the sclera of the eye. Many surgeons will place an absorbable suture around the tube at the time of surgery to prevent overfiltration through the device until a fibrous capsule has formed. Accordingly, such devices typically are not functional until about 3 to 8 weeks after the procedure, so as to prevent over-filtration.
An exemplary previously-known passive glaucoma drainage device is described in U.S. Pat. No. 4,457,757 to Molteno. The device described in that patent comprises a tube of a biologically inert silicone configured to be inserted into the eye to drain aqueous humor from the anterior chamber of the eye. The device does not include a pressure regulating mechanism, but instead relies on the resistance to aqueous flow through the tubing to prevent over drainage.
One drawback of devices such as those described in the Molteno patent is that the drainage flow depends on IOP and on the fixed hydrodynamic resistance of the shunt. In many cases, however, the hydrodynamic resistance of the shunt may not be sufficient to reduce high IOP when the resistance to flow is too high, or may lead to over-drainage if the resistance is low. For example, a common problem, which arises shortly after implantation, is hypotony, which occurs when IOP drops below acceptable physiological levels (i.e., IOP<10 mmHg). Hypotony usually takes place the first few days to weeks following the implantation of a glaucoma drainage device, and is a combined result of a low fluidic resistance of both the implant and the distal outflow paths. Hypotony may lead to a number of undesirable effects and complications, such as hypotensive maculopathy, cataract formation and optic nerve edema. Another problem, also related to the fixed fluid resistance of previously known implants, is fibrosis, which appears progressively at long term and which, depending on its extend and severity, may raise the effective fluidic resistance of the implant, thereby raising the IOP to different, often non-physiological, levels.
The foregoing drawbacks have been recognized in the prior art, and several improvements have been attempted to improve flow control over the entirely passive system described in Molteno.
For example, U.S. Pat. No. 5,411,473 to Ahmed describes is drainage device that includes membrane-type valve. More specifically, Ahmed describes a drainage system including a membrane folded and held in tension between two plates to provide a slit opening, such that the membrane responds to pressure changes to open or close the slit opening. Unfortunately, the operational characteristics of the system depend on the properties of the membrane, which cannot be changed easily once the device is implanted.
U.S. Pat. No. 5,300,020 to L'Esperance also describes a drainage system having a flow control element. In this patent, flow is controlled by a plug of absorbable material having porous properties that maintains anterior chamber pressure. Once aqueous humor has been absorbed into the plug, a path of relatively slow drainage flow will be established into the subconjunctival space until an equilibrium of pressures is developed. The pressure release is slow enough to avoid a collapse of the cornea yet sufficient to lower the intraocular pressure. Like the system described in Ahmed, the device described in L'Esperance includes the disadvantage that the porous material has fixed flow characteristics, and cannot be changed adapt to changes in the progression of the disease.
L'Esperance describes a further embodiment comprising a flexible drainage tube with a time-delay valve structure. The valve includes a ball biocompatible absorbable material that squeezes a portion of the drainage tube closed. As the absorbable material is dissolved by the aqueous humor, the squeezing force applied by the ball drops, progressively reducing the flow resistance of the drainage tube. In yet another embodiment, the time-delay valve comprises polymer components that either inherently, or due to the choice of composition, selectively shrink or stretch to effect opening and/or closure operation of the valve. In both of these latter embodiments, precise adjustment of the drainage flow rate is difficult to achieve, and once the valve control component has dissolved or changed shape further flow regulation is not possible.
Still other examples of previously-known systems are known. U.S. Pat. Nos. 5,626,558 and 6,508,779 to Suson describe a shunt which may be adjusted after implantation by using a low power laser to drill additional openings in the tube wall to adjust the flow rate. U.S. Pat. No. 6,186,974 to Allan et al. describes a drainage shunt having multiple layers, one of which may be a gel that swells upon absorption of fluid to adjust flow rate through the tube. U.S. Pat. No. 6,726,664 to Yaron describes a drainage tube including a distal hook that retains the distal end of the implant within the anterior chamber of the eye, and various means, such as rods or sutures, for partially occluding the lumen of the tube to regulate flow.
Other previously-known glaucoma treatment systems include significantly greater complexity to address the drawbacks of the simpler shunt systems described above. For example, U.S. Pat. No. 6,077,299 to Adelberg, et al. describes a non-invasively adjustable valved implant for the drainage of aqueous humor in glaucoma, wherein an implant having an inlet tube is surgically inserted in the anterior chamber of the eye to allow aqueous humor to flow from the anterior chamber to a valve. After passing through a pressure and/or flow regulating valve in the implant, the fluid is dispersed along the periphery of the implant to the interior of the Tenon's capsule where it is absorbed by the body. In one embodiment, the valve inhibits flow below, and allows flow above, a specific pressure difference between the intraocular pressure within the eye and the pressure within the bleb cavity in the Tenon's capsule. The specified pressure difference or set-point is always positive and the valve is always closed in the presence of negative pressure differences, to prevent reverse flow of fluid from the Tenon's capsule back into the anterior chamber of the eye.
In Adelberg, the valve is formed by a chamber to which the inlet tube is connected, such that the chamber is closed by a pressure sensitive valve in the shape of a flat cone. The pressure regulation set point of the valve is governed by a flexible diaphragm that cooperated with an armature plate having an inclined surface, and which is configured to slide over a complementary inclined surface attached to the diaphragm. Cooperation of the inclined surface of the plate and the complementary surface causes the diaphragm to deflect depending on where the armature plate is located. The armature plate is rotated, using a rotor and a set of speed-reducing and torque-enhancing gears, to regulate the flow through the device. The characteristics of the valve strongly depend on the configuration of the cone shaped valve. In addition, the regulating mechanism is complex, including many rotating parts and gears, and this complexity poses a risk of malfunction.
U.S. Pat. Nos. 6,168,575 and 6,589,198 to Soltanpour et al. describe micro-pump assemblies that may be implanted in the eye for controllably removing excess fluid to treat glaucoma. In these patents, the implantable pumps have a variable pumping rate that may be adjusted either manually or automatically, controlled by the measured intra-ocular pressure. However, these devices have the disadvantage of being complicated and expensive. In addition, because the implantable device contains electronics and a power source, such elements must be miniaturized to fit within in a suitably small sealed enclosure. As for the device described in Adelberg, the risk of malfunction also is high due to the large number of interacting elements present that must cooperate together.
Finally, WO 2009/066133 describes an ocular drainage system including a hollow chamber coupled to a drainage tube and a disk disposed within the hollow chamber. Flow from an exit hole of the drainage tube into the hollow chamber is controlled by rotating the disk to align a variable section slit on the disk with the exit hole. Fluid passing through the exit hole and the variable section slit into the hollow chamber is released outside of the implant. Flow through the device is adjusted by magnetically coupling an external adjustment device to the disk, which enables the disk to be rotated non-invasively. A drawback of the system described in this publication, however, is that large torques may be required to rotate the disk within the hollow chamber after implantation, due to deposit of proteinaceous materials from the aqueous humor.
In view of the drawbacks of the foregoing prior at devices and methods, it would be desirable to provide an ocular drainage system and methods that are capable of being non-invasively adjusted after implantation to control the hydraulic resistance of the device.
It further would be desirable to provide an ocular drainage system having few moving parts, thereby enhancing robustness of the system and reducing the risk of failure arising from having many complex, interacting parts.
It further would be desirable to provide an ocular drainage system and methods wherein moving parts of the system are configured to reduce the risk of clogging or becoming inoperative due to the buildup of proteinaceous sediments.
Finally, it would be desirable to provide an ocular drainage system and methods that permits the hydraulic resistance of the system to be periodically adjusted in a non-invasive manner.